https://codereview.appspot.com/579630043/diff/555740043/lily/stencil-integral.cc File lily/stencil-integral.cc (right):
https://codereview.appspot.com/579630043/diff/555740043/lily/stencil-integral.cc#newcode465 lily/stencil-integral.cc:465: // more convoluted, but it's fairly hot path. Sorry for not being clear: the question was not why this change was effective in saving time, but why it was valid. When thickness is zero, you only update the upper skyline. Why would the lower skyline no longer need updating? https://codereview.appspot.com/579630043/
